The present invention relates to a positive photosensitive composition which can be used as a photoresist in the manufacture of a semiconductor device and to a pattern forming method using the same.
Photoresist is used in the manufacture of electronic parts requiring various types of fine processing such as semiconductor integrated circuits like LSI. Also, a demagnificating projection type mask aligner, which is generally called stepper, is used as a light exposure apparatus for forming a resist pattern. The light source used in such a light exposure apparatus includes, for example, g-line (wavelength of 436 nm), h-line (wavelength of 405 nm), and i-line (wavelength of 365 nm) of a mercury lamp and an excimer laser light of KrF (wavelength of 248 nm), ArF (wavelength of 193 nm), F.sub.2 (wavelength of 157 nm), etc. Also, the exposure using an electron beam and an ion beam is an important technology in that, since the beam has a short wavelength, it is possible to achieve a fine processing, and in that a pattern can be formed directly. Such being the situation, it is of high importance to develop a resist adapted for such an exposure technology.
Formation of a fine pattern with a high through-put is absolutely necessary in recent years in accordance with progress in the degree of integration of semiconductor integrated circuit such as LSI. An electron beam lithography technology of a high sensitivity is also absolutely necessary as well as the resist material and process technology adapted for the lithography technology. However, the electron beam lithography necessitates a vacuum system, giving rise to problems derived from the use of the vacuum system. For example, resist containing an alkali soluble resin having an acetal group introduced therein as a protective group has a small activation energy for the deblocking reaction and, thus, is advantageous in that the resist exhibits a high sensitivity. However, where a resist film formed by coating a substrate with such a resist is irradiated with an electron beam, a layer which is unlikely to be dissolved in a developing solution is formed on the surface of the resist film, resulting in failure to form a resist pattern having a strict dimensional accuracy. In the worst case, the layer unlikely to be dissolved in the developing solution extends to cover an upper surface of the adjacent resist pattern, making it impossible to achieve resolution of the pattern.
In the light exposure using a KrF excimer laser light which does not require a vacuum system, the resist is affected by the condition such as humidity in the light exposure step after the resist coating step, making it difficult to form a resist pattern of a predetermined size at a predetermined sensitivity.